The invention starts with a system for interchanging business documents via communication networks, as described in the article "Edifakt will simplify electronic business communications" by Herbert C. Thomas, on pages 16 and 17 of the magazine "Computerwoche" (computer week) of Jun. 28, 1987.
With this system it is possible to interchange documents between different enterprises via electronic means. Such documents are e.g. invoices, orders or shipping memos. The interchange of such documents uses a worldwide standardized data format called Edifakt (Electronic Data Interchange for Administration, Commerce and Transport). This data format specifies e.g. how the syntax of a document must look or which data elements must be included for different business occasions.
It furthermore provides a number of standard messages that serve as the basis for the interchange of data for internationally structured business occasions.
The documents which correspond to the Edifakt data format are interchanged between enterprises by using an application protocol on layer 7 of the OSI reference model. This renders the transmission of data independent of the lower communication layers and thereby independent of the lower hardware and software being used. However, before documents can be transmitted, they must be converted from the data format in which they were created by the respective enterprise (in-house data format or customer-specific data format) to the Edifakt data format. This is necessary because the auxiliary means used to create documents, e.g. text processing programs, do not use the Edifakt data format as a rule. A large number of such customer-specific data formats exists.
This system for the electronic interchange of business documents has the disadvantage that both the sender as well as the recipient must have the necessary facilities for sending or receiving Edifakt documents. Since small enterprises in particular, and above all private persons, will not have such systems available within a foreseeable time, a large part of the business documents or the business mail must as before be printed in letter form and brought to the postal service, which then takes over the further delivery.
In addition electronic mail service facilities are known, such as described e.g. in patent DE 24 32 398.6. With such a facility it is possible to dispatch a letter to a postal recipient, where the letter travels part of the way as an electronic letter, i.e. in the form of a data block which is transmitted via a communication network.